1. Prior Art
Supplemental inflatable restraint ("SIR") sensors are positioned on motor vehicles and are responsive to the application of high impulse forces to initiate the deployment of air bags. In particular, in a majority of the motor vehicles at this time, there are one or more sensors placed at the very front of the vehicle, in as far forward a position as possible, to sense the application of an unusually high impact force such as that found when the front of the vehicle is involved in a crash. Another sensor may be typically placed on the firewall of the vehicle at the end of the engine compartment to sense the force application at that point. In such a system, both front sensors are electrically connected in parallel and then in series with the rearward sensor and one of the front and rearward sensors must be actuated substantially simultaneously in order for the air bag to be deployed.
Each motor vehicle platform has different characteristics for the transmittal of forces from the front of the vehicle to the passenger compartment. That is, the force necessary to deploy the air bag in small, light vehicles may be less than in larger, heavier vehicles. These forces are correlated to acceleration magnitudes of the vehicle. Typically when a motor vehicle is involved in a frontal crash, the acceleration of the vehicle as it stops is a function of the force being applied to the vehicle. Each sensor must respond to a designed acceleration pulse and must not respond to forces that are less both in time and amplitude.
When SIR sensors are manufactured, the force or acceleration response is designed into the sensor so that the sensor responds to a particular acceleration characteristic and does not respond to other acceleration characteristics. Once the sensor is manufactured, it is tested to determine that it meets the requirements.
Prior art testers are single sensor testers wherein one sensor is clamped into a particular position in a fixture and the testing acceleration characteristics are applied. The fixture is secured to a cross roller slide on a table of a thruster machine. The thruster machine operates to move the table in one direction at a high velocity and then reverses movement to get an acceleration signal. The single sensor must operate above one range and not operate below a lower range with a tolerance range therebetween where the sensor may or may not actuate. The ranges are different for sensors for different vehicle platforms. The mass of the slide, fixture and sensor device is limited by the operation specifications of the thruster machine. If the mass is too high, the acceleration pulses will not be correct and potentially good sensors will appear to be bad sensor. This error will not elevate a bad sensor to be a good sensor.
An example of such a sensor is that found in U.S. Pat. No. 4,329,549.